Light irradiation type heat treatment method

ABSTRACT

Heating treatment is performed on a semiconductor wafer in an ammonia atmosphere formed in a chamber by light irradiation from halogen lamps and flash lamps. For the formation of the ammonia atmosphere in the chamber, pressure in the chamber is once reduced. The pressure in the chamber is also reduced after the heating treatment of the semiconductor wafer. Light irradiation from the halogen lamps is performed to heat the atmosphere in the chamber before the pressure in the chamber is reduced by exhausting the atmosphere from the chamber. The heating of the atmosphere in the chamber before the pressure reduction activates the thermal motion of gas molecules in the atmosphere and decreases a gas density. As a result, the gas molecules in the chamber are discharged rapidly during the pressure reduction, so that the pressure in the chamber is reduced to a predetermined pressure in a short time.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a heat treatment method whichirradiates a thin plate-like precision electronic substrate (hereinafterreferred to simply as a “substrate”) such as a semiconductor wafer withlight to heat the substrate.

Description of the Background Art

In the process of manufacturing a semiconductor device, attention hasbeen given to flash lamp annealing (FLA) which heats a semiconductorwafer in an extremely short time. The flash lamp annealing is a heattreatment technique in which xenon flash lamps (the term “flash lamp” asused hereinafter refers to a “xenon flash lamp”) are used to irradiate asurface of a semiconductor wafer with a flash of light, thereby raisingthe temperature of only the surface of the semiconductor wafer in anextremely short time (several milliseconds or less).

The xenon flash lamps have a spectral distribution of radiation rangingfrom ultraviolet to near-infrared regions. The wavelength of lightemitted from the xenon flash lamps is shorter than that of light emittedfrom conventional halogen lamps, and approximately coincides with afundamental absorption band of a silicon semiconductor wafer. Thus, whena semiconductor wafer is irradiated with a flash of light emitted fromthe xenon flash lamps, the temperature of the semiconductor wafer can beraised rapidly, with only a small amount of light transmitted throughthe semiconductor wafer. Also, it has turned out that flash irradiation,that is, the irradiation of a semiconductor wafer with a flash of lightin an extremely short time of several milliseconds or less allows aselective temperature rise only near the surface of the semiconductorwafer.

Such flash lamp annealing is used for processes that require heating inan extremely short time, e.g. typically for the activation of impuritiesimplanted in a semiconductor wafer. The irradiation of a surface of asemiconductor wafer implanted with impurities by an ion implantationprocess with a flash of light emitted from flash lamps allows thetemperature rise only in the surface of the semiconductor wafer to anactivation temperature in an extremely short time, thereby achievingonly the activation of the impurities without deep diffusion of theimpurities.

On the other hand, an attempt has been made to perform the flash lampannealing in an atmosphere of a reactive gas such as ammonia. Forexample, U.S. Patent Application Publication No. 2017/0062249 disclosesthat an ammonia atmosphere is formed in a chamber which receives thereina semiconductor wafer with a high dielectric constant gate insulatorfilm (a high-k film) formed thereon and the semiconductor wafer isheated by irradiation with a flash of light, whereby post depositionanneal is performed on the high dielectric constant gate insulator film.In an apparatus disclosed in U.S. Patent Application Publication No.2017/0062249, the ammonia atmosphere is formed in the chamber bysupplying ammonia into the chamber after the pressure in the chamberwhich receives the semiconductor wafer therein is reduced. In theapparatus disclosed in U.S. Patent Application Publication No.2017/0062249, the semiconductor wafer already heat-treated in theammonia atmosphere is transported out of the chamber after thedetrimental ammonia is discharged and replaced with a nitrogenatmosphere by reducing the pressure in the chamber.

As disclosed in U.S. Patent Application Publication No. 2017/0062249,the formation of the atmosphere of the reactive gas such as ammonia forthe heating treatment of the semiconductor wafer requires the pressurereduction process to be performed twice, i.e. before and after theheating treatment Specifically, the pressure in the chamber is reducedbefore the formation of the ammonia atmosphere, and the pressure in thechamber is reduced also after the heating treatment for the purpose ofdischarging the ammonia. There are cases in which atmospheres of aplurality of treatment gases are formed in sequential order for thetreatment of a semiconductor wafer in some types of processes. In thesecases, the number of times of the pressure reduction process is furtherincreased. As a result, there arises a problem that a prolonged timeperiod required for the pressure reduction process increases the amountof time for treatment per semiconductor wafer to decrease throughput.

SUMMARY

The present invention is intended for a method of heating a substrate byirradiating the substrate with light.

According to one aspect of the present invention, the method comprisesthe steps of: (a) irradiating a substrate held by a susceptor in achamber with light from a continuous lighting lamp to preheat thesubstrate and thereafter irradiating the substrate with a flash of lightfrom a flash lamp to perform flash heating on the substrate; (b)exhausting an atmosphere from the chamber to reduce pressure in thechamber; and (c) performing light irradiation from the continuouslighting lamp to heat the atmosphere in the chamber, the step (c) beingperformed before the step (b).

This method activates the thermal motion of gas molecules in theatmosphere in the chamber and decreases a gas density. As a result, thepressure in the chamber is reduced in a short time.

Preferably, the step (c) is further performed continuously after thestart of the step (b).

This allows the pressure reduction in the chamber in a shorter time.

It is therefore an object of the present invention to reduce pressure ina chamber in a short period of time.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view showing a configuration of aheat treatment apparatus according to the present invention;

FIG. 2 is a perspective view showing the entire external appearance of aholder;

FIG. 3 is a plan view of a susceptor;

FIG. 4 is a sectional view of the susceptor,

FIG. 5 is a plan view of a transfer mechanism;

FIG. 6 is a side view of the transfer mechanism;

FIG. 7 is a plan view showing an arrangement of halogen lamps; and

FIG. 8 is a flow diagram showing a procedure for treatment of asemiconductor wafer according to a first preferred embodiment of thepresent invention;

FIG. 9 is a graph showing changes in pressure in a chamber, and

FIG. 10 is a flow diagram showing a procedure for atmosphere replacementin the chamber according to a second preferred embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments according to the present invention will now bedescribed in detail with reference to the drawings.

First Preferred Embodiment

FIG. 1 is a longitudinal sectional view showing a configuration of aheat treatment apparatus 1 according to the present invention. The heattreatment apparatus 1 of FIG. 1 is a flash lamp annealer for irradiatinga disk-shaped semiconductor wafer W serving as a substrate with flashesof light to heat the semiconductor wafer W. The size of thesemiconductor wafer W to be treated is not particularly limited. Forexample, the semiconductor wafer W to be treated has a diameter of 300mm and 450 mm (in the present preferred embodiment, 300 mm). A highdielectric constant film (a high-k film) serving as a gate insulatorfilm is formed on the semiconductor wafer W prior to the transport intothe heat treatment apparatus 1, and the heat treatment apparatus 1performs a heating treatment to thereby perform PDA (post depositionanneal) on the high dielectric constant film. It should be noted thatthe dimensions of components and the number of components are shown inexaggeration or in simplified form, as appropriate, in FIG. 1 and thesubsequent figures for the sake of easier understanding.

The heat treatment apparatus 1 includes a chamber 6 for receiving asemiconductor wafer W therein, a flash heating part 5 including aplurality of built-in flash lamps FL, and a halogen heating part 4including a plurality of built-in halogen lamps HL. The flash heatingpart 5 is provided over the chamber 6, and the halogen heating part 4 isprovided under the chamber 6. The heat treatment apparatus 1 furtherincludes a holder 7 provided inside the chamber 6 and for holding asemiconductor wafer W in a horizontal attitude, and a transfer mechanism10 provided inside the chamber 6 and for transferring a semiconductorwafer W between the holder 7 and the outside of the heat treatmentapparatus 1. The heat treatment apparatus 1 further includes acontroller 3 for controlling operating mechanisms provided in thehalogen heating part 4, the flash heating part 5, and the chamber 6 tocause the operating mechanisms to heat-treat a semiconductor wafer W.

The chamber 6 is configured such that upper and lower chamber windows 63and 64 made of quartz are mounted to the top and bottom, respectively,of a tubular chamber side portion 61. The chamber side portion 61 has agenerally tubular shape having an open top and an open bottom. The upperchamber window 63 is mounted to block the top opening of the chamberside portion 61, and the lower chamber window 64 is mounted to block thebottom opening thereof. The upper chamber window 63 forming the ceilingof the chamber 6 is a disk-shaped member made of quartz, and serves as aquartz window that transmits flashes of light emitted from the flashheating part 5 therethrough into the chamber 6. The lower chamber window64 forming the floor of the chamber 6 is also a disk-shaped member madeof quartz, and serves as a quartz window that transmits light emittedfrom the halogen heating part 4 therethrough into the chamber 6.

An upper reflective ring 68 is mounted to an upper portion of the innerwall surface of the chamber side portion 61, and a lower reflective ring69 is mounted to a lower portion thereof. Both of the upper and lowerreflective rings 68 and 69 are in the form of an annular ring. The upperreflective ring 68 is mounted by being inserted downwardly from the topof the chamber side portion 61. The lower reflective ring 69, on theother hand, is mounted by being inserted upwardly from the bottom of thechamber side portion 61 and fastened with screws not shown. In otherwords, the upper and lower reflective rings 68 and 69 are removablymounted to the chamber side portion 61. An interior space of the chamber6, i.e. a space surrounded by the upper chamber window 63, the lowerchamber window 64, the chamber side portion 61, and the upper and lowerreflective rings 68 and 69, is defined as a heat treatment space 65.

A recessed portion 62 is defined in the inner wall surface of thechamber 6 by mounting the upper and lower reflective rings 68 and 69 tothe chamber side portion 61. Specifically, the recessed portion 62 isdefined which is surrounded by a middle portion of the inner wallsurface of the chamber side portion 61 where the reflective rings 68 and69 are not mounted, a lower end surface of the upper reflective ring 68,and an upper end surface of the lower reflective ring 69. The recessedportion 62 is provided in the form of a horizontal annular ring in theinner wall surface of the chamber 6, and surrounds the holder 7 whichholds a semiconductor wafer W. The chamber side portion 61 and the upperand lower reflective rings 68 and 69 are made of a metal material (e.g.,stainless steel) with high strength and high heat resistance.

The chamber side portion 61 is provided with a transport opening(throat) 66 for the transport of a semiconductor wafer W therethroughinto and out of the chamber 6. The transport opening 66 is openable andclosable by a gate valve 185. The transport opening 66 is connected incommunication with an outer peripheral surface of the recessed portion62. Thus, when the transport opening 66 is opened by the gate valve 185,a semiconductor wafer W is allowed to be transported through thetransport opening 66 and the recessed portion 62 into and out of theheat treatment space 65. When the transport opening 66 is closed by thegate valve 185, the heat treatment space 65 in the chamber 6 is anenclosed space.

The chamber side portion 61 is further provided with a through hole 61 abored therein. A radiation thermometer 20 is mounted to a location of anouter wall surface of the chamber side portion 61 where the through hole61 a is provided. The through hole 61 a is a cylindrical hole fordirecting infrared radiation emitted from the lower surface of asemiconductor wafer W held by a susceptor 74 to be described latertherethrough to the radiation thermometer 20. The through hole 61 a isinclined with respect to a horizontal direction so that a longitudinalaxis (an axis extending in a direction in which the through hole 61 aextends through the chamber side portion 61) of the through hole 61 aintersects a main surface of the semiconductor wafer W held by thesusceptor 74. A transparent window 21 made of barium fluoride materialtransparent to infrared radiation in a wavelength range measurable withthe radiation thermometer 20 is mounted to an end portion of the throughhole 61 a which faces the heat treatment space 65.

At least one gas supply opening 81 for supplying a treatment gas (in thepresent preferred embodiment, nitrogen gas (N₂) and/or ammonia (NH₃))therethrough into the heat treatment space 65 is provided in an upperportion of the inner wall of the chamber 6. The gas supply opening 81 isprovided above the recessed portion 62, and may be provided in the upperreflective ring 68. The gas supply opening 81 is connected incommunication with a gas supply pipe 83 through a buffer space 82provided in the form of an annular ring inside the side wall of thechamber 6. The gas supply pipe 83 is divided into two branch pipes. Oneof the two branch pipes is a reactive gas pipe 83 a connected to anammonia supply source 91, and the other is an inert gas pipe 83 bconnected to a nitrogen supply source 92. The ammonia supply source 91feeds ammonia to the reactive gas pipe 83 a under the control of thecontroller 3. The nitrogen supply source 92 feeds nitrogen gas to theinert gas pipe 83 b under the control of the controller 3.

A supply source valve 93, a supply check pressure gauge 94, a mass flowcontroller 95, and a supply valve 96 are interposed in the reactive gaspipe 83 a. When the supply source valve 93 and the supply valve 96 areopened, ammonia is fed from the ammonia supply source 91 through thereactive gas pipe 83 a and the gas supply pipe 83 to the buffer space82. The supply check pressure gauge 94 judges whether ammonia issupplied at a predetermined pressure from the ammonia supply source 91through the reactive gas pipe 83 a or not. The mass flow controller 95regulates the flow rate of ammonia flowing through the reactive gas pipe83 a to a predetermined set value.

On the other hand, a mass flow controller 97 and a supply valve 98 areinterposed in the inert gas pipe 83 b. When the supply valve 98 isopened, nitrogen gas is fed from the nitrogen supply source 92 throughthe inert gas pipe 83 b and the gas supply pipe 83 to the buffer space82. The mass flow controller 97 regulates the flow rate of nitrogen gasflowing through the inert gas pipe 83 b to a predetermined set value.When all of the supply source valve 93, the supply valve 96, and thesupply valve 98 are open, ammonia fed from the reactive gas pipe 83 aand nitrogen gas fed from the inert gas pipe 83 b are joined together inthe gas supply pipe 83, so that a gas mixture of ammonia and nitrogengas is fed to the buffer space 82.

A bypass pipe 84 for connecting the reactive gas pipe 83 a and the inertgas pipe 83 b to each other for communication therebetween is furtherprovided. The bypass pipe 84 connects a portion of the reactive gas pipe83 a which lies between the supply source valve 93 and the supply checkpressure gauge 94 and a portion of the inert gas pipe 83 b which liesbetween the nitrogen supply source 92 and the mass flow controller 97 toeach other for communication therebetween. A bypass valve 85 isinterposed in the bypass pipe 84. When the bypass valve 85 is opened,the reactive gas pipe 83 a and the inert gas pipe 83 b are brought intocommunication with each other.

The treatment gas fed from the gas supply pipe 83 and flowing in thebuffer space 82 flows in a spreading manner within the buffer space 82which is lower in fluid resistance than the gas supply opening 81 tofill the buffer space 82. Then, the treatment gas filling the bufferspace 82 is supplied through the gas supply opening 81 into the heattreatment space 65.

At least one gas exhaust opening 86 for exhausting a gas from the heattreatment space 65 is provided in a lower portion of the inner wall ofthe chamber 6. The gas exhaust opening 86 is provided below the recessedportion 62, and may be provided in the lower reflective ring 69. The gasexhaust opening 86 is connected in communication with a gas exhaust pipe88 through a buffer space 87 provided in the form of an annular ringinside the side wall of the chamber 6. The gas exhaust pipe 88 isconnected to an exhaust part 190. An exhaust valve 89 and a vacuumpressure gauge 191 are interposed in the gas exhaust pipe 88. When theexhaust valve 89 is opened, the gas in the heat treatment space 65 isexhausted through the gas exhaust opening 86 and the buffer space 87 tothe gas exhaust pipe 88. The vacuum pressure gauge 191 measures thepressure in the gas exhaust pipe 88 directly. The pressure measured bythe vacuum pressure gauge 191 is the pressure in the chamber 6 becausethe pressure in a portion of the gas exhaust pipe 88 where the vacuumpressure gauge 191 is provided is approximately equal to the pressure inthe chamber 6. The at least one gas supply opening 81 and the at leastone gas exhaust opening 86 may include a plurality of gas supplyopenings 81 and a plurality of gas exhaust openings 86, respectively,arranged in a circumferential direction of the chamber 6, and may be inthe form of slits.

A vacuum pump and a utility exhaust system in a factory in which theheat treatment apparatus 1 is installed may be used as the exhaust part190. When a vacuum pump is employed as the exhaust part 190 to exhaustthe atmosphere provided in the heat treatment space 65 which is anenclosed space while no gas is supplied from the gas supply opening 81,the atmosphere provided in the chamber 6 is reduced in pressure to avacuum atmosphere. When the vacuum pump is not used as the exhaust part190, the pressure of the atmosphere provided in the chamber 6 is reducedto a pressure lower than atmospheric pressure by exhausting theatmosphere provided in the heat treatment space 65 while the gas is notsupplied from the gas supply opening 81. The pressure in the chamber 6which is being reduced is measured by the vacuum pressure gauge 191.

FIG. 2 is a perspective view showing the entire external appearance ofthe holder 7. The holder 7 includes a base ring 71, coupling portions72, and the susceptor 74. The base ring 71, the coupling portions 72,and the susceptor 74 are all made of quartz. In other words, the wholeof the holder 7 is made of quartz.

The base ring 71 is a quartz member having an arcuate shape obtained byremoving a portion from an annular shape. This removed portion isprovided to prevent interference between transfer arms 11 of thetransfer mechanism 10 to be described later and the base ring 71. Thebase ring 71 is supported by the wall surface of the chamber 6 by beingplaced on the bottom surface of the recessed portion 62 (with referenceto FIG. 1). The multiple coupling portions 72 (in the present preferredembodiment, four coupling portions 72) are mounted upright on the uppersurface of the base ring 71 and arranged in a circumferential directionof the annular shape thereof. The coupling portions 72 are quartzmembers, and are rigidly secured to the base ring 71 by welding.

The susceptor 74 is supported by the four coupling portions 72 providedon the base ring 71. FIG. 3 is a plan view of the susceptor 74. FIG. 4is a sectional view of the susceptor 74. The susceptor 74 includes aholding plate 75, a guide ring 76, and a plurality of substrate supportpins 77. The holding plate 75 is a generally circular planar member madeof quartz. The diameter of the holding plate 75 is greater than that ofa semiconductor wafer W. In other words, the holding plate 75 has asize, as seen in plan view, greater than that of the semiconductor waferW.

The guide ring 76 is provided on a peripheral portion of the uppersurface of the holding plate 75. The guide ring 76 is an annular memberhaving an inner diameter greater than the diameter of the semiconductorwafer W. For example, when the diameter of the semiconductor wafer W is300 mm, the inner diameter of the guide ring 76 is 320 mm. The innerperiphery of the guide ring 76 is in the form of a tapered surface whichbecomes wider in an upward direction from the holding plate 75. Theguide ring 76 is made of quartz similar to that of the holding plate 75.The guide ring 76 may be welded to the upper surface of the holdingplate 75 or fixed to the holding plate 75 with separately machined pinsand the like. Alternatively, the holding plate 75 and the guide ring 76may be machined as an integral member.

A region of the upper surface of the holding plate 75 which is insidethe guide ring 76 serves as a planar holding surface 75 a for holdingthe semiconductor wafer W. The substrate support pins 77 are providedupright on the holding surface 75 a of the holding plate 75. In thepresent preferred embodiment, a total of 12 substrate support pins 77are spaced at intervals of 30 degrees along the circumference of acircle concentric with the outer circumference of the holding surface 75a (the inner circumference of the guide ring 76). The diameter of thecircle on which the 12 substrate support pins 77 are disposed (thedistance between opposed ones of the substrate support pins 77) issmaller than the diameter of the semiconductor wafer W, and is 270 to280 mm (in the present preferred embodiment, 270 mm) when the diameterof the semiconductor wafer W is 300 mm. Each of the substrate supportpins 77 is made of quartz. The substrate support pins 77 may be providedby welding on the upper surface of the holding plate 75 or machinedintegrally with the holding plate 75.

Referring again to FIG. 2, the four coupling portions 72 providedupright on the base ring 71 and the peripheral portion of the holdingplate 75 of the susceptor 74 are rigidly secured to each other bywelding. In other words, the susceptor 74 and the base ring 71 arefixedly coupled to each other with the coupling portions 72. The basering 71 of such a holder 7 is supported by the wall surface of thechamber 6, whereby the holder 7 is mounted to the chamber 6. With theholder 7 mounted to the chamber 6, the holding plate 75 of the susceptor74 assumes a horizontal attitude (an attitude such that the normal tothe holding plate 75 coincides with a vertical direction). In otherwords, the holding surface 75 a of the holding plate 75 becomes ahorizontal surface.

A semiconductor wafer W transported into the chamber 6 is placed andheld in a horizontal attitude on the susceptor 74 of the holder 7mounted to the chamber 6. At this time, the semiconductor wafer W issupported by the 12 substrate support pins 77 provided upright on theholding plate 75, and is held by the susceptor 74. More strictlyspeaking, the 12 substrate support pins 77 have respective upper endportions coming in contact with the lower surface of the semiconductorwafer W to support the semiconductor wafer W. The semiconductor wafer Wis supported in a horizontal attitude by the 12 substrate support pins77 because the 12 substrate support pins 77 have a uniform height(distance from the upper ends of the substrate support pins 77 to theholding surface 75 a of the holding plate 75).

The semiconductor wafer W supported by the substrate support pins 77 isspaced a predetermined distance apart from the holding surface 75 a ofthe holding plate 75. The thickness of the guide ring 76 is greater thanthe height of the substrate support pins 77. Thus, the guide ring 76prevents the horizontal misregistration of the semiconductor wafer Wsupported by the substrate support pins 77.

As shown in FIGS. 2 and 3, an opening 78 is provided in the holdingplate 75 of the susceptor 74 so as to extend vertically through theholding plate 75 of the susceptor 74. The opening 78 is provided for theradiation thermometer 20 to receive radiation (infrared radiation)emitted from the lower surface of the semiconductor wafer W.Specifically, the radiation thermometer 20 receives the radiationemitted from the lower surface of the semiconductor wafer W through theopening 78 and the transparent window 21 mounted to the through hole 61a in the chamber side portion 61 to measure the temperature of thesemiconductor wafer W. Further, the holding plate 75 of the susceptor 74further includes four through holes 79 bored therein and designed sothat lift pins 12 of the transfer mechanism 10 to be described laterpass through the through holes 79, respectively, to transfer asemiconductor wafer W.

FIG. 5 is a plan view of the transfer mechanism 10. FIG. 6 is a sideview of the transfer mechanism 10. The transfer mechanism 10 includesthe two transfer arms 11. The transfer arms 11 are of an arcuateconfiguration extending substantially along the annular recessed portion62. Each of the transfer arms 11 includes the two lift pins 12 mountedupright thereon. The transfer arms 11 and the lift pins 12 are made ofquartz. The transfer arms 11 are pivotable by a horizontal movementmechanism 13. The horizontal movement mechanism 13 moves the pair oftransfer arms 1′1 horizontally between a transfer operation position (aposition indicated by solid lines in FIG. 5) in which a semiconductorwafer W is transferred to and from the holder 7 and a retracted position(a position indicated by dash-double-dot lines in FIG. 5) in which thetransfer arms 11 do not overlap the semiconductor wafer W held by theholder 7 as seen in plan view. The horizontal movement mechanism 13 maybe of the type which causes individual motors to pivot the transfer arms11 respectively or of the type which uses a linkage mechanism to cause asingle motor to pivot the pair of transfer arms 11 in cooperativerelation.

The transfer arms 11 are moved upwardly and downwardly together with thehorizontal movement mechanism 13 by an elevating mechanism 14. As theelevating mechanism 14 moves up the pair of transfer arms 11 in theirtransfer operation position, the four lift pins 12 in total pass throughthe respective four through holes 79 (with reference to FIGS. 2 and 3)bored in the susceptor 74, so that the upper ends of the lift pins 12protrude from the upper surface of the susceptor 74. On the other hand,as the elevating mechanism 14 moves down the pair of transfer arms 11 intheir transfer operation position to take the lift pins 12 out of therespective through holes 79 and the horizontal movement mechanism 13moves the pair of transfer arms 11 so as to open the transfer arms 11,the transfer arms 11 move to their retracted position. The retractedposition of the pair of transfer arms 11 is immediately over the basering 71 of the holder 7. The retracted position of the transfer arms 11is inside the recessed portion 62 because the base ring 71 is placed onthe bottom surface of the recessed portion 62. An exhaust mechanism notshown is also provided near the location where the drivers (thehorizontal movement mechanism 13 and the elevating mechanism 14) of thetransfer mechanism 10 are provided, and is configured to exhaust anatmosphere around the drivers of the transfer mechanism 10 to theoutside of the chamber 6.

The heat treatment apparatus 1 further includes an atmospherethermometer 28 for measuring the atmosphere temperature in the chamber6, and a radiation thermometer 29 for measuring the temperature of thesusceptor 74. The atmosphere thermometer 28 is constructed using athermocouple, for example. The radiation thermometer 29 receivesinfrared radiation emitted from the susceptor 74 made of quartz tomeasure the temperature of the susceptor 74, based on the intensity ofthe received infrared radiation.

Referring again to FIG. 1, the flash heating part 5 provided over thechamber 6 includes an enclosure 51, a light source provided inside theenclosure 51 and including the multiple (in the present preferredembodiment, 30) xenon flash lamps FL, and a reflector 52 provided insidethe enclosure 51 so as to cover the light source from above. The flashheating part 5 further includes a lamp light radiation window 53 mountedto the bottom of the enclosure 51. The lamp light radiation window 53forming the floor of the flash heating part 5 is a plate-like quartzwindow made of quartz. The flash heating part is provided over thechamber 6, whereby the lamp light radiation window 53 is opposed to theupper chamber window 63. The flash lamps FL direct flashes of light fromover the chamber 6 through the lamp light radiation window 53 and theupper chamber window 63 toward the heat treatment space 65.

The flash lamps FL, each of which is a rod-shaped lamp having anelongated cylindrical shape, are arranged in a plane so that thelongitudinal directions of the respective flash lamps FL are in parallelwith each other along a main surface of a semiconductor wafer W held bythe holder 7 (that is, in a horizontal direction). Thus, a plane definedby the arrangement of the flash lamps FL is also a horizontal plane. Aregion in which the flash lamps FL are arranged has a size, as seen inplan view, greater than that of the semiconductor wafer W.

Each of the xenon flash lamps FL includes a rod-shaped glass tube(discharge tube) containing xenon gas sealed therein and having positiveand negative electrodes provided on opposite ends thereof and connectedto a capacitor, and a trigger electrode attached to the outer peripheralsurface of the glass tube. Because the xenon gas is electricallyinsulative, no current flows in the glass tube in a normal state even ifelectrical charge is stored in the capacitor. However, if a high voltageis applied to the trigger electrode to produce an electrical breakdown,electricity stored in the capacitor flows momentarily in the glass tube,and xenon atoms or molecules are excited at this time to cause lightemission. Such a xenon flash lamp FL has the property of being capableof emitting extremely intense light as compared with a light source thatstays lit continuously such as a halogen lamp HL because theelectrostatic energy previously stored in the capacitor is convertedinto an ultrashort light pulse ranging from 0.1 to 100 milliseconds.Thus, the flash lamps FL are pulsed light emitting lamps which emitlight instantaneously for an extremely short time period of less thanone second. The light emission time of the flash lamps FL is adjustableby the coil constant of a lamp light source which supplies power to theflash lamps FL.

The reflector 52 is provided over the plurality of flash lamps FL so asto cover all of the flash lamps FL. A fundamental function of thereflector 52 is to reflect flashes of light emitted from the pluralityof flash lamps FL toward the heat treatment space 65. The reflector 52is a plate made of an aluminum alloy. A surface of the reflector 52 (asurface which faces the flash lamps FL) is roughened by abrasiveblasting.

The halogen heating part 4 provided under the chamber 6 includes anenclosure 41 incorporating the multiple (in the present preferredembodiment, 40) halogen lamps HL. The halogen heating part 4 is a lightirradiator that directs light from under the chamber 6 through the lowerchamber window 64 toward the heat treatment space 65 to heat thesemiconductor wafer W by means of the halogen lamps HL.

FIG. 7 is a plan view showing an arrangement of the multiple halogenlamps HL. The 40 halogen lamps HL are arranged in two tiers, i.e. upperand lower tiers. That is, halogen lamps HL are arranged in the uppertier closer to the holder 7, and 20 halogen lamps HL are arranged in thelower tier farther from the holder 7 than the upper tier. Each of thehalogen lamps HL is a rod-shaped lamp having an elongated cylindricalshape. The 20 halogen lamps HL in each of the upper and lower tiers arearranged so that the longitudinal directions thereof are in parallelwith each other along a main surface of a semiconductor wafer W held bythe holder 7 (that is, in a horizontal direction). Thus, a plane definedby the arrangement of the halogen lamps HL in each of the upper andlower tiers is also a horizontal plane.

As shown in FIG. 7, the halogen lamps HL in each of the upper and lowertiers are disposed at a higher density in a region opposed to aperipheral portion of the semiconductor wafer W held by the holder 7than in a region opposed to a central portion thereof. In other words,the halogen lamps HL in each of the upper and lower tiers are arrangedat shorter intervals in a peripheral portion of the lamp arrangementthan in a central portion thereof. This allows a greater amount of lightto impinge upon the peripheral portion of the semiconductor wafer Wwhere a temperature decrease is prone to occur when the semiconductorwafer W is heated by the irradiation thereof with light from the halogenheating part 4.

The group of halogen lamps HL in the upper tier and the group of halogenlamps HL in the lower tier are arranged to intersect each other in alattice pattern. In other words, the 40 halogen lamps HL in total aredisposed so that the longitudinal direction of the 20 halogen lamps HLarranged in the upper tier and the longitudinal direction of the 20halogen lamps HL arranged in the lower tier are orthogonal to eachother.

Each of the halogen lamps HL is a filament-type light source whichpasses current through a filament disposed in a glass tube to make thefilament incandescent, thereby emitting light. A gas prepared byintroducing a halogen element (iodine, bromine and the like) in traceamounts into an inert gas such as nitrogen, argon and the like is sealedin the glass tube. The introduction of the halogen element allows thetemperature of the filament to be set at a high temperature whilesuppressing a break in the filament. Thus, the halogen lamps HL have theproperties of having a longer life than typical incandescent lamps andbeing capable of continuously emitting intense light. That is, thehalogen lamps HL are continuous lighting lamps that emit lightcontinuously for not less than one second. In addition, the halogenlamps HL, which are rod-shaped lamps, have a long life. The arrangementof the halogen lamps HL in a horizontal direction provides goodefficiency of radiation toward the semiconductor wafer W provided overthe halogen lamps HL.

A reflector 43 is provided also inside the enclosure 41 of the halogenheating part 4 under the halogen lamps HL arranged in two tiers (FIG.1). The reflector 43 reflects the light emitted from the halogen lampsHL toward the heat treatment space 65.

The controller 3 controls the aforementioned various operatingmechanisms provided in the heat treatment apparatus 1. The controller 3is similar in hardware configuration to a typical computer.Specifically, the controller 3 includes a CPU that is a circuit forperforming various computation processes, a ROM or read-only memory forstoring a basic program therein, a RAM or readable/writable memory forstoring various pieces of information therein, and a magnetic disk forstoring control software, data and the like thereon. The CPU in thecontroller 3 executes a predetermined processing program, whereby theprocesses in the heat treatment apparatus 1 proceed.

The heat treatment apparatus 1 further includes, in addition to theaforementioned components, various cooling structures to prevent anexcessive temperature rise in the halogen heating part 4, the flashheating part 5, and the chamber 6 because of the heat energy generatedfrom the halogen lamps HL and the flash lamps FL during the heattreatment of a semiconductor wafer W. As an example, a water coolingtube (not shown) is provided in the walls of the chamber 6. Also, thehalogen heating part 4 and the flash heating part 5 have an air coolingstructure for forming a gas flow therein to exhaust heat. Air issupplied to a gap between the upper chamber window 63 and the lamp lightradiation window 53 to cool down the flash heating part 5 and the upperchamber window 63.

Next, a treatment operation in the heat treatment apparatus 1 will bedescribed. FIG. 8 is a flow diagram showing a procedure for treatment ofa semiconductor wafer W according to a first preferred embodiment of thepresent invention. The semiconductor wafer W to be treated herein is asilicon semiconductor substrate with a high dielectric constant filmformed thereon as a gate insulator film. The high dielectric constantfilm is deposited on the front surface of the semiconductor wafer W, forexample, by a technique including ALD (atomic layer deposition), MOCVD(metal organic chemical vapor deposition), and the like. The heattreatment apparatus 1 irradiates the semiconductor wafer W with a flashof light in an ammonia atmosphere to perform PDA (post depositionanneal) on the semiconductor wafer W, thereby eliminating defects in thedeposited high dielectric constant film. The procedure for the treatmentin the heat treatment apparatus 1 to be described below proceeds underthe control of the controller 3 over the operating mechanisms of theheat treatment apparatus 1.

First, the semiconductor wafer W with the high dielectric constant filmformed thereon is transported into the chamber 6 of the heat treatmentapparatus 1 (Step S11). For the transport of the semiconductor wafer Winto the chamber 6, the gate valve 185 is opened to open the transportopening 66. A transport robot outside the heat treatment apparatus 1transports the semiconductor wafer W with the high dielectric constantfilm formed thereon through the transport opening 66 into the heattreatment space 65 of the chamber 6. At this time, an atmosphere outsidethe heat treatment apparatus 1 is carried into the heat treatment space65 of the chamber 6 as the semiconductor wafer W is transported into theheat treatment space 65 because the pressure inside and outside thechamber 6 is equal to atmospheric pressure. To prevent this, nitrogengas may be continuously supplied from the nitrogen supply source 92 intothe chamber 6 by opening the supply valve 98 to cause the nitrogen gasto flow outwardly through the opened transport opening 66, therebyminimizing the atmosphere outside the heat treatment apparatus 1 flowinginto the chamber 6. It is further preferable that the exhaust valve 89is closed to stop exhausting the gas from the chamber 6 when the gatevalve 185 is open. This causes the nitrogen gas supplied into thechamber 6 to flow outwardly only through the transport opening 66,thereby effectively preventing the outside atmosphere from flowing intothe chamber 6.

The semiconductor wafer W transported into the heat treatment space 65by the transport robot is moved forward to a position lying immediatelyover the holder 7 and is stopped thereat. Then, the pair of transferarms 11 of the transfer mechanism 10 is moved horizontally from theretracted position to the transfer operation position and is then movedupwardly, whereby the lift pins 12 pass through the through holes 79 andprotrude from the upper surface of the holding plate 75 of the susceptor74 to receive the semiconductor wafer W. At this time, the lift pins 12move upwardly to above the upper ends of the substrate support pins 77.

After the semiconductor wafer W is placed on the lift pins 12, thetransport robot moves out of the heat treatment space 65, and the gatevalve 185 closes the transport opening 66. Then, the pair of transferarms 11 moves downwardly to transfer the semiconductor wafer W from thetransfer mechanism 10 to the susceptor 74 of the holder 7, so that thesemiconductor wafer W is held in a horizontal attitude from below. Thesemiconductor wafer W is supported by the substrate support pins 77provided upright on the holding plate 75, and is held by the susceptor74. The semiconductor wafer W is held by the holder 7 in such anattitude that the front surface thereof where the high dielectricconstant film is deposited is the upper surface. A predetermineddistance is defined between the back surface (a main surface oppositefrom the front surface) of the semiconductor wafer W supported by thesubstrate support pins 77 and the holding surface 75 a of the holdingplate 75. The pair of transfer arms 11 moved downwardly below thesusceptor 74 is moved back to the retracted position, i.e. to the insideof the recessed portion 62, by the horizontal movement mechanism 13.

After the semiconductor wafer W is received in the chamber 6 and thetransport opening 66 is closed by the gate valve 185, pressure in thechamber 6 is reduced to a pressure lower than atmospheric pressure. FIG.9 is a graph showing changes in pressure in the chamber 6. In FIG. 9,the abscissa represents time, and the ordinate represents pressure inthe chamber 6. At a point of time t1 when the semiconductor wafer W isreceived in the chamber 6 and the transport opening 66 is closed, thepressure in the chamber 6 is equal to ordinary pressure Ps (=atmosphericpressure=approximately 101325 Pa).

In the first preferred embodiment, the atmosphere in the chamber 6 isheated by irradiation with light from the halogen lamps HL of thehalogen heating part 4 (Step S12) at time t2 before the pressurereduction in the chamber 6. Part of light emitted from the halogen lampsHL is directly absorbed by gas molecules of the atmosphere in thechamber 6, so that the temperature of the atmosphere is increased. Partof light emitted from the halogen lamps HL is also absorbed by thesemiconductor wafer W held by the susceptor 74, so that the temperatureof the atmosphere in the chamber 6 is increased also by heat transferfrom the heated semiconductor wafer W.

The temperature of the atmosphere in the chamber 6 is measured with theatmosphere thermometer 28 when the atmosphere in the chamber 6 is heatedby irradiation with light from the halogen lamps HL. The temperature ofthe atmosphere in the chamber 6 measured with the atmosphere thermometer28 is transmitted to the controller 3. The controller 3 effects feedbackcontrol of the output from the halogen lamps HL so that the temperatureof the atmosphere in the chamber 6 is equal to a target temperature TP,based on the value measured with the atmosphere thermometer 28. The rateof increase in temperature of the atmosphere in the chamber 6 and thetarget temperature TP are not particularly limited. For example, therate of increase in temperature is 20° C./sec, and the targettemperature TP is 250° C. That is, the controller 3 effects feedbackcontrol of the output from the halogen lamps HL so that the valuemeasured with the atmosphere thermometer 28 is increased to 250° C. at arate of 20° C./sec.

The pressure reduction in the chamber 6 is started (Step S13) at time t3after the temperature of the atmosphere in the chamber 6 reaches thetarget temperature TP. Specifically, the transport opening 66 is closed,so that the heat treatment space 65 of the chamber 6 becomes an enclosedspace. In this state, the exhaust valve 89 is opened while the supplyvalve 96 and the supply valve 98 for supplying the gas are closed. Thus,the gas is exhausted from the chamber 6 while the gas is not suppliedinto the chamber 6, so that the pressure in the heat treatment space 65of the chamber 6 is reduced to less than atmospheric pressure. In anearly stage of the pressure reduction, the exhaust part 190 exhausts theatmosphere from the chamber 6 at a relatively low exhaust flow rate toreduce the pressure in the chamber 6.

Next, at time t4 when the pressure in the chamber 6 measured by thevacuum pressure gauge 191 is reduced to a pressure P1, the exhaust flowrate of the atmosphere exhausted by the exhaust part 190 increases, sothat the exhaust speed thereof becomes faster. The pressure P1 is, forexample, approximately 20000 Pa. At time t5, the pressure (degree ofvacuum) in the chamber 6 reaches a pressure P2. The pressure P2 is, forexample, approximately 100 Pa. That is, after the atmosphere isexhausted at a low exhaust flow rate in the early stage of the pressurereduction, the exhaust flow rate is changed to a higher exhaust flowrate, and the atmosphere is exhausted at the higher exhaust flow rate.

If the atmosphere is exhausted rapidly at a high exhaust flow rate atthe start of the pressure reduction, there is a danger that a large gasflow change occurs in the chamber 6 to cause particles deposited onstructures (e.g., the lower chamber window 64) in the chamber 6 to swirlup and be deposited again on the semiconductor wafer W, resulting incontamination of the semiconductor wafer W. Such particles in thechamber 6 are prevented from swirling up by exhausting the atmospherecalmly at a low exhaust flow rate in the early stage of the pressurereduction, thereafter changing the exhaust flow rate to a higher exhaustflow rate, and exhausting the atmosphere at the higher exhausted flowrate.

At the time t5 when the pressure in the chamber 6 reaches the pressureP2, the supply of the treatment gas into the chamber 6 is started (StepS14). Specifically, the supply source valve 93, the supply valve 96, andthe supply valve 98 are opened while the exhaust valve 89 is open.Specifically, ammonia is fed from the reactive gas pipe 83 a by openingthe supply source valve 93 and the supply valve 96. Also, nitrogen gasis fed from the inert gas pipe 83 b by opening the supply valve 98. Thefed ammonia and nitrogen gas are joined together in the gas supply pipe83. Then, a gas mixture of ammonia and nitrogen gas is supplied into theheat treatment space 65 of the chamber 6. As a result, an ammoniaatmosphere in a reduced-pressure condition is formed around thesemiconductor wafer W held by the holder 7 in the chamber 6. Theconcentration of ammonia in the ammonia atmosphere (i.e., the mixtureratio between ammonia and nitrogen gas) is not particularly limited butmay have an appropriate value. For example, the concentration of ammoniais required only to be not greater than 10 vol. % (in the presentpreferred embodiment, approximately 2.5 vol. %). The concentration ofammonia is adjustable by controlling the supply flow rates of ammoniaand nitrogen gas by means of the mass flow controller 95 and the massflow controller 97, respectively.

By supplying the gas mixture of ammonia and nitrogen gas into thechamber 6, the pressure in the chamber 6 is increased from the pressureP2 to reach a pressure P3 at time t6. The pressure P3 is, for example,approximately 5000 Pa. The oxygen concentration in the ammoniaatmosphere formed in the chamber 6 is made extremely low because thepressure in the chamber 6 is reduced once to the pressure P2 and thenincreased to the pressure P3. After the time t6 when the pressure in thechamber 6 is increased to the pressure P3, the supply flow rate of theammonia-nitrogen gas mixture into the chamber 6 and the exhaust flowrate thereof from the chamber 6 are made equal to each other, so thatthe pressure in the chamber 6 is maintained at the pressure P3.

Next, the heating treatment of the semiconductor wafer W is performed(Step S15) after the time t6 when the pressure in the chamber 6 isincreased to the pressure P3. First, the semiconductor wafer W ispreheated (assist-heated) by irradiation with light from the 40 halogenlamps HL in the halogen heating part 4. Halogen light emitted from thehalogen lamps HL is transmitted through the lower chamber window 64 andthe susceptor 74 both made of quartz, and impinges upon the lowersurface of the semiconductor wafer W. By receiving light irradiationfrom the halogen lamps HL, the semiconductor wafer W is preheated, sothat the temperature of the semiconductor wafer W increases. It shouldbe noted that the transfer arms 11 of the transfer mechanism 10, whichare retracted to the inside of the recessed portion 62, do not become anobstacle to the heating using the halogen lamps HL.

The temperature of the semiconductor wafer W is measured with theradiation thermometer 20 when the halogen lamps HL perform thepreheating. Specifically, the radiation thermometer 20 receives infraredradiation emitted from the lower surface of the semiconductor wafer Wheld by the susceptor 74 through the opening 78 and passing through thetransparent window 21 to measure the temperature of the semiconductorwafer W which is on the increase. The measured temperature of thesemiconductor wafer W is transmitted to the controller 3. The controller3 controls the output from the halogen lamps HL while monitoring whetherthe temperature of the semiconductor wafer W which is on the increase bythe irradiation with light from the halogen lamps HL reaches apredetermined preheating temperature T1 or not. In other words, thecontroller 3 effects feedback control of the output from the halogenlamps HL so that the temperature of the semiconductor wafer W is equalto the preheating temperature T1, based on the value measured with theradiation thermometer 20. The preheating temperature T1 is in the rangeof 300° to 600° C., and is 450° C. in the present preferred embodiment.

After the temperature of the semiconductor wafer W reaches thepreheating temperature T1, the controller 3 maintains the temperature ofthe semiconductor wafer W at the preheating temperature T1 for a shorttime. Specifically, at the point in time when the temperature of thesemiconductor wafer W measured with the radiation thermometer reachesthe preheating temperature T1, the controller 3 adjusts the output fromthe halogen lamps HL to maintain the temperature of the semiconductorwafer W at approximately the preheating temperature T1.

By performing such preheating using the halogen lamps HL, thetemperature of the entire semiconductor wafer W is uniformly increasedto the preheating temperature T1. In the stage of preheating using thehalogen lamps HL, the semiconductor wafer W shows a tendency to be lowerin temperature in a peripheral portion thereof where heat dissipation isliable to occur than in a central portion thereof. However, the halogenlamps HL in the halogen heating part 4 are disposed at a higher densityin the region opposed to the peripheral portion of the semiconductorwafer W than in the region opposed to the central portion thereof. Thiscauses a greater amount of light to impinge upon the peripheral portionof the semiconductor wafer W where heat dissipation is liable to occur,thereby providing a uniform in-plane temperature distribution of thesemiconductor wafer W in the stage of preheating.

The flash lamps FL in the flash heating part 5 irradiate the frontsurface of the semiconductor wafer W held by the susceptor 74 with aflash of light at time t7 when a predetermined time period has elapsedsince the temperature of the semiconductor wafer W reached thepreheating temperature T1. At this time, part of the flash of lightemitted from the flash lamps FL travels directly toward the interior ofthe chamber 6. The remainder of the flash of light is reflected oncefrom the reflector 52, and then travels toward the interior of thechamber 6. The irradiation of the semiconductor wafer W with suchflashes of light achieves the flash heating of the semiconductor waferW.

The flash heating, which is achieved by the emission of a flash of lightfrom the flash lamps FL, is capable of increasing the front surfacetemperature of the semiconductor wafer W in a short time. Specifically,the flash of light emitted from the flash lamps FL is an intense flashof light emitted for an extremely short period of time ranging fromabout 0.1 to about 100 milliseconds as a result of the conversion of theelectrostatic energy previously stored in the capacitor into such anultrashort light pulse. By irradiating the front surface of thesemiconductor wafer W with the high dielectric constant film depositedthereon with a flash of light from the flash lamps FL, the temperatureof the front surface of the semiconductor wafer W including the highdielectric constant film momentarily increases to a treatmenttemperature T2, so that the PDA is performed. The treatment temperatureT2 that is the maximum temperature (peak temperature) reached by thefront surface of the semiconductor wafer W subjected to the flashirradiation is in the range of 600° to 1200° C., and is 1000° C. in thepresent preferred embodiment.

The PDA performed by the increase in temperature of the front surface ofthe semiconductor wafer W to the treatment temperature T2 in the ammoniaatmosphere promotes the nitriding of the high dielectric constant filmand eliminates defects such as point defects present in the highdielectric constant film. The time period for the irradiation with lightfrom the flash lamps FL is a short time period ranging from about 0.1 toabout 100 milliseconds. Accordingly, the time required for thetemperature of the front surface of the semiconductor wafer W toincrease from the preheating temperature T1 to the treatment temperatureT2 is also an extremely short time period of less than one second.Immediately after the flash irradiation, the temperature of the frontsurface of the semiconductor wafer W rapidly decreases from thetreatment temperature T2.

After the completion of the flash heating treatment, the atmosphere inthe chamber 6 is heated again by irradiation with light from the halogenlamps HL at time t8 (Step S16). As in Step S12, the atmosphere in thechamber 6 is heated directly by the irradiation with light from thehalogen lamps HL, and is in addition heated indirectly by the heattransfer from the heated semiconductor wafer W. Also, the controller 3effects feedback control of the output from the halogen lamps HL so thatthe temperature of the atmosphere in the chamber 6 is equal to thetarget temperature TP, based on the value measured with the atmospherethermometer 28.

At time t9 after the temperature of the atmosphere in the chamber 6reaches the target temperature TP, the reduction in pressure in thechamber 6 starts (Step S17). Specifically, the exhaust valve 89 isopened while the supply valve 96 and the supply valve 98 are closed.This exhausts the atmosphere from the chamber 6 to reduce the pressurein the chamber 6 again. The pressure in the chamber 6 reaches thepressure P2 at time t10. The pressure in the chamber 6 is reduced to thepressure P2 again by exhausting the atmosphere from the chamber 6,whereby the detrimental ammonia is discharged from the heat treatmentspace 65 of the chamber 6.

Subsequently, the exhaust valve 89 is closed and the supply valve 98 isopened, so that the nitrogen gas is supplied as the inert gas from thenitrogen supply source 92 into the chamber 6 to return the pressure inthe chamber 6 to the ordinary pressure Ps (Step S18). Thus, theatmosphere in the chamber 6 is replaced with a nitrogen atmosphere. Thehalogen lamps HL turn off. This causes the temperature of thesemiconductor wafer W to decrease also from the preheating temperatureT1. The radiation thermometer 20 measures the temperature of thesemiconductor wafer W which is on the decrease. The result ofmeasurement is transmitted to the controller 3. The controller 3monitors whether the temperature of the semiconductor wafer W isdecreased to a predetermined temperature or not, based on the result ofmeasurement. After the temperature of the semiconductor wafer W isdecreased to the predetermined temperature or below, the pair oftransfer arms 11 of the transfer mechanism 10 is moved horizontallyagain from the retracted position to the transfer operation position andis then moved upwardly, so that the lift pins 12 protrude from the uppersurface of the susceptor 74 to receive the heat-treated semiconductorwafer W from the susceptor 74. Subsequently, the transport opening 66which has been closed is opened by the gate valve 185, and the transportrobot outside the heat treatment apparatus 1 transports thesemiconductor wafer W placed on the lift pins 12 to the outside. Thus,the heat treatment apparatus 1 completes the heating treatment of thesemiconductor wafer W (Step S19).

In the first preferred embodiment, the atmosphere in the chamber 6 isheated by the irradiation with light from the halogen lamps HL beforethe pressure in the chamber 6 is reduced by exhausting the atmospherefrom the chamber 6 during the treatment of the semiconductor wafer W(Steps S12 and S16). The heating of the atmosphere in the chamber 6before the pressure reduction activates the thermal motion of the gasmolecules in the atmosphere and decreases a gas density. As a result,the gas molecules in the chamber 6 are discharged rapidly during thepressure reduction, so that the pressure in the chamber 6 is reduced toa predetermined pressure in a short time. This suppresses the increasein time for treatment of the semiconductor wafer W involving thepressure reduction process to prevent throughput from decreasing.

In the first preferred embodiment, the atmosphere in the chamber 6 isheated by the irradiation with light from the halogen lamps HL, with thesemiconductor wafer W present in the chamber 6. The temperature of thesemiconductor wafer W is lower than the aforementioned preheatingtemperature T1 when the temperature of the atmosphere in the chamber 6is equal to the target temperature TP. Thus, there is no danger that theirradiation with light from the halogen lamps HL for the pressurereduction process exerts significant influence on the heat treatmenthistory of the semiconductor wafer W.

Second Preferred Embodiment

Next, a second preferred embodiment according to the present inventionwill be described. The second preferred embodiment is similar inconfiguration of the heat treatment apparatus 1 and in procedure fortreatment of the semiconductor wafer W to the first preferredembodiment. In the first preferred embodiment, the atmosphere in thechamber 6 is heated and the pressure reduction process is then performedduring the treatment of the semiconductor wafer W, i.e. before and afterthe flash heating while the semiconductor wafer W is held by thesusceptor 74. In the second preferred embodiment, on the other hand, theatmosphere in the chamber 6 is heated and the pressure reduction processis then performed at the time of the maintenance of the heat treatmentapparatus 1.

Maintenance is performed on the aforementioned heat treatment apparatus1 at regular or irregular time intervals. Irregular maintenance isperformed when some failure occurs in the heat treatment apparatus 1.The interior of the chamber 6 is opened and the various pipes aredetached from the heat treatment apparatus 1 at the time of themaintenance of the heat treatment apparatus 1, regardless of whether themaintenance is regular or irregular. It is hence necessary thatdetrimental ammonia is completely discharged from the entire heattreatment apparatus 1 including the heat treatment space 65 of thechamber 6 and the various pipes before the maintenance. To this end, thesupply valve 96 is opened to discharge the ammonia also from thereactive gas pipe 83 a in addition to the heat treatment space 65 of thechamber 6.

FIG. 10 is a flow diagram showing a procedure for atmosphere replacementin the chamber 6 according to the second preferred embodiment. First,light irradiation from the halogen lamps HL is performed to heat theatmosphere in the chamber 6 in the absence of a semiconductor wafer W inthe chamber 6 before maintenance (Step S21). Part of light emitted fromthe halogen lamps HL is directly absorbed by gas molecules of theatmosphere in the chamber 6, so that the atmosphere is directly heated.Part of light emitted from the halogen lamps HL is also absorbed by thestructures such as the susceptor 74 in the chamber 6, so that theatmosphere in the chamber 6 is indirectly heated by the heat transferfrom the structures.

The temperature of the atmosphere in the chamber 6 is measured with theatmosphere thermometer 28 when the atmosphere in the chamber 6 is heatedby irradiation with light from the halogen lamps HL. The temperature ofthe atmosphere in the chamber 6 measured with the atmosphere thermometer28 is transmitted to the controller 3. In the second preferredembodiment, the halogen lamps HL are turned on with constant electricpower (for example, fixed at 30% of maximum electric power) to heat theatmosphere in the chamber 6 until the temperature of the atmosphere inthe chamber 6 reaches the target temperature TP. That is, although theoutput from the halogen lamps HL is feedback-controlled in the firstpreferred embodiment, constant output control is effected in the secondpreferred embodiment. The target temperature TP of the atmosphere in thechamber 6 is, for example, 250° C. as in the first preferred embodiment.

The pressure reduction in the chamber 6 is started (Step S22) after thetemperature of the atmosphere in the chamber 6 reaches the targettemperature TP. Specifically, the supply source valve 93, the bypassvalve 85, and the supply valve 98 are closed, whereas the supply valve96 and the exhaust valve 89 are opened. Thus, the atmosphere in thechamber 6 and in the reactive gas pipe 83 a including the mass flowcontroller 95 (precisely, a region of the reactive gas pipe 83 a whichis downstream of the supply source valve 93) is exhausted through thegas exhaust pipe 88, so that not only the pressure in the chamber 6 butalso the pressure in the reactive gas pipe 83 a is reduced. As a result,ammonia remaining in the reactive gas pipe 83 a is also discharged.

Next, after the pressure in the chamber 6 measured by the vacuumpressure gauge 191 is reduced to a predetermined pressure, the pressurereduction is stopped, and the supply of the nitrogen gas into thereactive gas pipe 83 a and the chamber 6 is performed (Step S23). Atthis time, the supply source valve 93 and the exhaust valve 89 areclosed, whereas the supply valve 96, the supply valve 98, and the bypassvalve 85 are opened. Thus, part of the nitrogen gas fed from thenitrogen supply source 92 is charged through the bypass pipe 84 into thereactive gas pipe 83 a including the mass flow controller 95 (precisely,a region of the reactive gas pipe 83 a which lies between the supplysource valve 93 and the supply valve 96). The nitrogen gas fed from thenitrogen supply source 92 is also charged into the chamber 6.

After the nitrogen gas is charged into the chamber 6 and the reactivegas pipe 83 a, the procedure proceeds to Step S24, in which thecontroller 3 determines whether the aforementioned pressure reductionprocess and the nitrogen gas supply have been repeated a set number oftimes or not. The number of times of repetition is previously set in thecontroller 3, for example, using a GUI (graphical user interface). Whenthe pressure reduction process and the nitrogen gas supply have not yetbeen repeated the set number of times, the pressure reduction process inStep S22 and the nitrogen gas supply in Step S23 are repeated again. Forexample, when the number of times of repetition is set to “10”, theaforementioned pressure reduction process and the nitrogen gas supplyare repeated ten times. Thus, the ammonia is discharged from thereactive gas pipe 83 a and the chamber 6 with reliability, and thenitrogen gas is charged into the reactive gas pipe 83 a and the chamber6.

In the second preferred embodiment, the atmosphere in the chamber 6 isheated by the irradiation with light from the halogen lamps HL and thepressure in the chamber 6 is then reduced by exhausting the atmospherefrom the chamber 6 before the maintenance of the heat treatmentapparatus 1. The heating of the atmosphere in the chamber 6 before thepressure reduction activates the thermal motion of the gas molecules inthe atmosphere and decreases the gas density. As a result, the gasmolecules in the chamber 6 are discharged rapidly during the pressurereduction, so that the pressure in the chamber 6 is reduced to apredetermined pressure in a short time, as in the first preferredembodiment. This allows the reduction in time required for the nitrogengas purge before the maintenance.

<Modifications>

While the preferred embodiments according to the present invention havebeen described hereinabove, various modifications of the presentinvention in addition to those described above may be made withoutdeparting from the scope and spirit of the invention. For example, theatmosphere in the chamber 6 is heated before the pressure in the chamber6 is reduced in the first and second preferred embodiments. In additionto this, the atmosphere in the chamber 6 may be heated by theirradiation with light from the halogen lamps HL continuously after thestart of the pressure reduction in the chamber 6. The heating of theatmosphere in the chamber 6 by the irradiation with light from thehalogen lamps HL also after the start of the pressure reduction in thechamber 6 allows the pressure reduction in a shorter period of time.Alternatively, the heating of the atmosphere in the chamber 6 by theirradiation with light from the halogen lamps HL may be started afterthe start of the pressure reduction in the chamber 6.

In the first preferred embodiment, the output from the halogen lamps HLis feedback-controlled. In place of this, the halogen lamps HL may beturned on with constant electric power to heat the atmosphere in thechamber 6 until the temperature of the atmosphere in the chamber 6reaches the target temperature TP, as in the second preferredembodiment. In the second preferred embodiment, on the other hand, theoutput from the halogen lamps HL may be feedback-controlled so that thetemperature of the atmosphere in the chamber 6 is equal to the targettemperature TP, based on the value measured with the atmospherethermometer 28. That is, whether to effect feedback control or constantoutput control of the output from the halogen lamps HL may be selected,as appropriate. Alternatively, the feedback control and the constantoutput control may be combined together. As an example, the constantoutput control of the output from the halogen lamps HL may be effectedwhile the temperature of the atmosphere in the chamber 6 is relativelylow, whereas the feedback control of the output from the halogen lampsHL is effected after the temperature of the atmosphere in the chamber 6approaches the target temperature TP.

Also, the feedback control of the output from the halogen lamps HL maybe effected based on the temperature of the susceptor 74 measured withthe radiation thermometer 29 or the temperature of the semiconductorwafer W measured with the radiation thermometer 20 in place of thetemperature of the atmosphere in the chamber 6. However, the feedbackcontrol of the output from the halogen lamps HL based on the temperatureof the atmosphere in the chamber 6 measured with the atmospherethermometer 28 as in the first preferred embodiment enables thetemperature of the atmosphere in the chamber 6 to be equal to the targettemperature TP more directly.

In the aforementioned preferred embodiments, ammonia is supplied throughthe reactive gas pipe 83 a. The present invention, however, is notlimited to this. Oxygen (O₂), hydrogen (H₂), chlorine (Cl₂), hydrogenchloride (HCl), ozone (O₃), nitrogen monoxide (NO), nitrous oxide (N₂O),nitrogen dioxide (NO₂), nitrogen trifluoride (NF₃) or the like may besupplied as the reactive gas through the reactive gas pipe 83 a. The gassupplied through the inert gas pipe 83 b is not limited to nitrogen gas.Argon (Ar), helium (He) or the like may be supplied as the inert gasthrough the inert gas pipe 83 b.

In the first preferred embodiment, the heating treatment of thesemiconductor wafer W is performed while the ammonia atmosphere isformed in the chamber 6. However, a plurality of types of differentatmospheres may be formed in the chamber 6 in succession for thetreatment of the semiconductor wafer W. In this case, the pressure inthe chamber 6 is reduced a plurality of times during the treatment ofone semiconductor wafer W. Thus, the technique according to the presentinvention may be well applied to reduce the pressure in the chamber 6every time in a short time, thereby shortening the treatment time.

Although the 30 flash lamps FL are provided in the flash heating part 5according to the aforementioned preferred embodiments, the presentinvention is not limited to this. Any number of flash lamps FL may beprovided. The flash lamps FL are not limited to the xenon flash lamps,but may be krypton flash lamps. Also, the number of halogen lamps HLprovided in the halogen heating part 4 is not limited to 40. Any numberof halogen lamps HL may be provided.

In the aforementioned preferred embodiments, the filament-type halogenlamps HL are used as continuous lighting lamps that emit lightcontinuously for not less than one second to preheat the semiconductorwafer W. The present invention, however, is not limited to this. Inplace of the halogen lamps HL, discharge type arc lamps (e.g., xenon arclamps) may be used as the continuous lighting lamps to perform thepreheating. In this case, the atmosphere in the chamber 6 is heated bylight irradiation from the are lamps before the pressure reductionprocess.

Moreover, a substrate to be treated by the heat treatment apparatus 1 isnot limited to a semiconductor wafer, but may be a glass substrate foruse in a flat panel display for a liquid crystal display apparatus andthe like, and a substrate for a solar cell. Also, the heat treatmentapparatus 1 may perform the activation of implanted impurities, thejoining of metal and silicon, and the crystallization of polysilicon.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the invention.

What is claimed is:
 1. A method of heating a substrate by irradiatingthe substrate with light, comprising the steps of: (a) irradiating asubstrate held by a susceptor in a chamber with light from a continuouslighting lamp to preheat said substrate and thereafter irradiating saidsubstrate with a flash of light from a flash lamp to perform flashheating on said substrate; (b) exhausting an atmosphere from saidchamber to reduce pressure in said chamber; and (c) performing lightirradiation from said continuous lighting lamp to heat the atmosphere insaid chamber; wherein said steps (b) and (c) are performed before andafter said step (a).
 2. The method according to claim 1, wherein saidstep (c) is further performed continuously after the start of said step(b).
 3. The method according to claim 1, wherein said steps (b) and (c)are performed, with said substrate held by said susceptor in saidchamber.
 4. The method according to claim 1, wherein said steps (b) and(c) are performed in the absence of said substrate in said chamber. 5.The method according to claim 4, wherein said steps (b) and (c) areperformed before maintenance of said chamber.
 6. The method according toclaim 1, wherein said continuous lighting lamp is turned on withconstant electric power to heat the atmosphere in said chamber in saidstep (c).
 7. The method according to claim 1, wherein feedback controlof an output from said continuous lighting lamp is effected based on thetemperature of the atmosphere in said chamber or the temperature of saidsusceptor in said step (c).